FN 503 IWB Holster Our FN 503 holster was designed and crafted using our high-tech proprietary process to exacting specifications. We’re so confident in our IWB holsters that we back them up with a lifetime warranty and 30-day free returns. The Base FN 503 IWB holster is designed for EDC and all-day comfort. It can be worn cross-draw, appendix, strong side, or all the way to small of back. Our FN 503 Holster fully protects the trigger and mag release for ultimate safety while carrying .